DNA and RNA constitute the key molecular components of all genetic processes, and have similar structural components. DNA typically exists as a complex of two anti-parallel linear strands or sequences of deoxyribonucleotide structural units, each unit of which consists of a nitrogenous base (adenine (A), thymidine (T), cytosine (C) or guanine (G)), a pentose sugar (a 5-carbon sugar), and a phosphate group. RNA is typically single stranded, and uses uracil (U) in place of thymidine (T). Moreover, the pentose sugar in DNA is 2-deoxyribose, while the pentose sugar in RNA is ribose. The nitrogenous bases of DNA and RNA are of two classes: the larger nine-member double-ring purines, A and G, and smaller six-member single-ring pyrimidines, C, T and U.
The polymerase chain reaction (PCR) presents a very effective method for selectively amplifying specific DNA fragments. In the PCR procedure, oligonucleotides complementary to known segments of the target DNA fragment are added as “primers.” The primers serve as starting point for DNA replication enabling PCR amplification. Often, sequencing tags can be included in the primer as a way to identify and or track a gene transcript.
Sequencing of DNA and RNA is an important analytical technique for generating genetic information from biological sources. Sequencing has made possible the determination of DNA and RNA sequences of entire genomes. It is an important diagnostic tool in the clinic, where the rapid detection of a single nucleobase change or a few nucleobase changes can be used to detect, for example, a genetic disease.